Dry eye syndrome is one of the most frequent diseases in the field of ophthalmology, the prevalence increasing with age. According to the definition by the “Dry Eye Workshop Study Group” (DEWS Steering Committee), the dry eye syndrome is a multifactorial disturbance of the tear film and eye surface, which is accompanied by physical-psychic discomfort or visual impairment. Inflammatory processes and a hyperosmolar tear film are important factors associated with this clinical picture.
The clinical picture of the dry eye is often understood to be keratoconjunctivitis sicca. “Keratoconjunctivitis sicca” refers to a disease of the eye surface accompanied by typical symptoms, such as a foreign body sensation, light sensitivity, itching, burning pain, and a feeling of pressure. In addition, visual reduction, reddened eyes, epiphora (constant tearing) and a dry eye sensation are often observed. When the tear production is reduced, the complaints occur preferentially in the morning. If the problem resides in an increased evaporation of the lacrimal fluid, the symptoms occur more frequently in the evening.
Today, a wide variety of artificial tear substitutes in the form of eye drops, eye gel or eye spray are offered for treating dry eye syndrome. For example, there may be mentioned the replacement or supplementing of the aqueous phase of the lacrimal fluid by aqueous solutions of thickening agents, such as povidone, hyproxymellose or carboxymethylcellulose, salts and optionally further active substances, such as hyaluronic acid or lipids. Also known is the supplementing of the surface lipid layer of the tear film by a liposomal eye spray, which reduces the evaporation of the natural lacrimal fluid and avoids premature draining as a tear beyond the lash line. Further known is the replacement of the tear film and the reduction of the shear forces between the eye surface and lid during the lid movements by fat-containing ointments. In particular, such ointments are oil-in-water emulsions.
A disadvantage of these known products is the fact that they have a relatively short dwelling time on the cornea. This is the reason why the corresponding treating agent must be applied on a regular basis, which is often unpleasant for the patient, or even impossible in some situations. For example, in a distinctly dry eye, one drop each of an aqueous phase should be dripped into either eye every 30 to 60 minutes, in order to compensate for existing deficits. With treating agents in gel form, this drawback is avoided at least in part. However, it is found difficult here to supply the cornea sufficiently with oxygen. In addition, just like with ointments, the vision may be impaired for some seconds or even minutes. If the corresponding agents include preservatives, these may lead to allergic responses on the one hand. In addition, when permanently and frequently applied, this may lead to a deterioration of the dry eye symptoms.
Further, the use of punctal plugs is known. When the lacrimal fluid produced by the lacrimal gland is drained to the nose, the lacrimal fluid is initially distributed by blinks over the cornea in order to keep it wet. Subsequently, it is drained from the conjunctival sac through the lacrimal puncta (puncta lacrimalia). Punctal plugs are inserted into one or both lacrimal puncta to reduce this drain. Depending on their nature, the plugs may permanently remain in the lacrimal puncta, or dissolve after a few weeks. The essential disadvantage of this method is the fact that the retaining of the lacrimal fluid at the same time also causes the inflammation-promoting substances in the lacrimal fluid, which has an altered composition in dry eyes, to remain longer on the eye. In addition, the draining of lacrimal fluid through the effluent tear ducts, which is reduced by the plugs, may promote infections by bacteria that may ascend from the nasal cavity.
Especially in pronounced diseases of the eye surface, it was found that the known artificial tear substitutes or the use of punctal plugs not necessarily leads to the desired success. The artificial tear substitutes always contain only some components of natural tears. A sustainable therapy is hardly possible in such a case.
A relatively new approach in the therapy of diseases of the eye surface includes the use of eye drops made from serum, especially the patient's own serum. An advantage thereof is the fact that corresponding eye drops have some biomechanical and biochemical similarity with the lacrimal fluid. The therapeutic success here is better than that obtained with otherwise usually employed artificial tear substitutes, as shown by E. M. Herold (“Therapie der Keratokonjunktivitis Sicca mit Augentropfen aus autologem Serum”, Inaugural Dissertation of Erlangen Nürnberg University, Dec. 20, 2012). The patient's own serum means autologous serum obtained from the blood of the person who later employs the eye drops prepared therefrom.